This invention relates to the field of panoramic conical mirrors, and particularly to the design and production of panoramic convex conical mirrors for statically viewing any prescribed vertical field of view.
An orthographic mirror is a mirror in which all incoming rays are reflected normal to the imaging plane. Existing designs of orthographic mirrors, such as that described by Nayar in U.S. Pat. No. 5,760,826, utilize the standard equation of a parabola limiting the linearity of the images scene to at best 93%. In addition, this approach is also limited to a constant field of view of 90xc2x0, ranging from 0xc2x0 which is the z=0 plane, to 90xc2x0 which is typically the position of the imaging system above or below the panoramic mirrored cone element. This arrangement produces a panoramic image in which about 25% of the image is unusable since it falls outside this 90xc2x0 field of view.
Improvements to this design include incorporating a shifted parabola to define the mirrored surface and allowing the field of view to be adjusted based on specific needs of the application the mirror is designed for. Adjustments to the defined field of view can be accomplished by adjusting the vertical incident angles or by adjusting the radial positions corresponding to the angle limits. These adjustments do result in a linearity higher than that achieved by the pure parabola, but there is still room for improvement.
Commonly-invented, commonly-assigned U.S. Pat. No. 6,028,719, issued Feb. 22, 2000, describes use of a panoramic mirrored cone element such as, but not limited to mirrored element of the present disclosure, in an imaging; apparatus that achieves both 360 degree peripheral and forward viewing in a single plane.
Therefore, it is desirable to provide an improved orthographic mirrored element design.
It is also desirable to provide an improved panoramic conical mirrored element design for statically viewing any prescribed vertical field of view with a scene vertical angle to the image""s radial position that achieves linearity greater than 99%.
It is also desirable to provide a means for panoramic imaging of both positive and negative viewing angles, and generally increasing the overall field of view.
Disclosed herein is an improvement in the design of orthographic panoramic mirrored optical elements. By designing a panoramic mirrored cone element as herein disclosed, a linearity greater than 99% can be achieved. The present invention is based on the ability to iteratively improve on the basic parabolic design by making modifications that approach spherical and/or elliptical designs. Testing the linearity of the panoramic imaging element""s design is a major part of the iterative process since each element is designed based on application-specific parameters. The improved design allows for the extension of the vertical filed of view to span the range of +70xc2x0 to xe2x88x9245xc2x0 while retaining high linearity greater than 99%.